Acylation of amino stilbene sulfonic acids



mustb ,carried ut in Patented Aug. 7, I951 OFFICE ACYLATION OF AMINO STILBENE SULFONIC ACIDS Wendell Philip Munro, Martinsville, N. J., assignor to American Cyanamid Company, New

York, N. Y., a corporation of Maine N Drawing. Application July 7, 1949, Serial No. 103,541

Claims.

This inventionis concerned with the preparation of certain stilbenederivatives. More particularly, it relates to a process for acylating amino sulfonic acids" of the stilbene series. Specifically, the invention is concerned with an improved acid binder for the hydrogen halide acid which is formed in acylating amino stilbene sulfonic acids with anaroyl halide.

Amino stilbeiie sulf onic acids, especially 4,4- diamino-stilbene-2,2'-disu1fonic acid, are important dyestuff intermediates. In addition, it has been found more recently that several of the acyl derivativesof'the latter possess special properties. Theyare highly effective optical bleach- 13% agents or brighteners in overcoming the yellowishfcast, which is found in, or developed by, many so-called white cellulosic materials.

A number of methods, none wholly satisfactory, have been suggested for the preparation of these acylated derivatives. In the past, the greatest difiiculty hasbeenthat direct acylation with an acid halide cannotbe accomplished particularly well,.either in-an aquequs'medium solution or in an organic solvent. More recently, an improved method has been developed. An aqueous medium is used, the mediumcontaining in addition to.water,,specified.proportions of certain ketonic'solvents.'j I H I ,Whatever. the "particular process used, so long as av reaction is carried out between an aroyl halide and anamino stilbenesulfonic acid, a hydrogen halide. acid i corresponding to the aroyl halide is ormeid. Thisacid must be taken up "or neutralized in someway, inord'er that the reaction 'productmay besuccessiully formed and subsequently'recovered. It is withj-the solution of this acid removal problem that the present invention is concerned. c

In general, incases ofthis kind, there is considered to be little choice between'acid-accepting agents. It would ordinarily be presumed thatan agent such as soda ash or an agent such as potash,

would be substantially interchangeable. Accord ingly, because soda ash is more commonly available, and ordinarily,considerably cheaper, it is regularlyusedr: f. In attempting direct acylation of 4,-4'-diaminosti1bene-2,2-disulfonioacid with a benzoyl halide, 1 suchfor example as ortho-methoxy benzoyl-chloride, it was found. that a large excess oi-the acid halide is required; This makes the process-bothexpensive and wasteful. Itcomplicates: product isolation h andv purification, which the presence of relatively large amounts 0 a aromatiqacid resulting from hydrolysis of the excess acid halide. Unfortunately, if these conditions were not observed it was found that the product yield was not particularly satisfactory. At least, this was the finding when attempts were made to carry out the re-i action in the conventional way, using a sodium salt of a weak acid or sodium hydroxide as the acid-accepting agent. I

In accordance with the present invention,-it has been found that, for some reason, potash is particularly beneficial. It is not subject to limitations and conditions, which are found in the use of soda ash; There appears to be no particu-. larly good explanation-0f this phenomenon and accordingly, the present invention is not intended to be limited to any particular theory of opera--.

tion.

Use of potash as the neutralizing agent has a number of advantages. First and most noticeable, it causes a direct increase in the yield. Secs 0nd and almost equally important, for some reason much less acid halide is required to carry out a successful reaction when potash is present. Instead of the large excesses :formerly required,

only a moderate excess is now found necessary.

This advantage is particularly significant in the case of one of thealkoxy benzoyl-chlorides, which are very suspectible to hydrolysis, and with this important class of acid chlorides our invention is particularly useful.

It is an important further advantage of the present method that the use of potashas contrasted with the prior'use of soda ash makes the reaction surprisingly insensitive to the purity of this acid chloride, and/or its freedom from impurities normally inherent'inits production, such as salicyclic acid and thionyl chloride.

This is of very definite advantage. Using soda ash, acylation of a material such as 4,4-diamin'ostilbene-2,2'-disulfonic acid, with ortho-methoxyand ortho-ethoxybenzoyl chloride, is found to be very seriously afiected' by small amounts of impurities, such as salicylic. acid or'its chloride. In the methods used in the art, presence of some salicyclic acid or its chloride is almost inevitable. This is due to the fact, that in the alkylation of salicyclic acid, the resulting alkyl ethers usually contain small amounts of salicyclic acid, since the alkylation reaction is veryv diflicult to force to completion. I

In general, the process as carried out in accordance with the present, invention, is quite simple. Direct reaction is readily carried out. It is pref.- erable to keep .the temperature below Iordinary room temperature, in order to minimize ide reactions, but satisfactory results can be obtained at temperatures up to about 40 C. Furthermore, the precise proportions of potash is not particularly critical. A suiiicient excess is used, so that the reaction medium is never permitted to become acidic. More than this amount has no particular benefit.

It has also been found that the use of potash, in accordance with the present invention, can be combined with the use of ketonic solvents, such as described in the copending application of Eberhart et al., Serial No. 24,107, filed April 28, 1948, now abandoned. When using both potash and a ketonic solvent in this manner, superior results are obtained to those which can be obtained by the use of either alone.

A highly suitable method of operation is to dissolve the amino stilbene sulfonic acid in an aqueous potash solution, to add thereto the ketonic solvent, if one is to be used; and then to add the aroyl halide. The latter is preferably added slowly, with continuous agitation. Temperature, as noted above, should be maintained below 40 C. In the case of the exemplary 4,4'-diamino-stilbene-2,2-disulfonic acid, the desired acylation product separates from solution in excellent yield in the form of its di-potassium salt.

It has been found that the present invention may be applied with the halides of benzoic acid and its substitution products, such as the isomeric toluic acids, and their higher homologues, halobenzoic acids, nitrobenzoic acids, acylaminobenzoic acids, azodiand azoxydi-benzoic acids, and cyanobenzoic acids. More than one substituent may be present. These substituents may be the same, as for example in dichlorobenzoic acids, or different as in nitrotoluic acids. It has been found that particularly advantageous results are obtained with alkoxybenzoic acids, such as anisic acid, salicylic acid methyl. ether, ortho-ethoxybenzoic acid, 2,3-dimethoxybenzoic acid, and the like. 1

Incarrying out the reaction, one factor may be noted. Amino stilbenes. such as 4,4-diamino- 2,2'-disulfonic acid are not readily soluble in water per se. Their alkali metal salts, however, are quite soluble. It is not necessary to start the reaction with the potassium salt. For example, the acid may be added to water and dissolved by the addition of an equivalent amount of caustic soda or caustic potash. The novelty of the present invention lies in the use of potash, over and above the alkali required to dissolve the amino stilbene sulfonic acid, as an acid-accepting agent.

The present invention will be more fully illustrated. in conjunction with the following examples. These examples are given solely by way of. illustration. Except as otherwise noted, all parts are by weight and all temperature degrees centigrade.

' Example 1 cooled to '8-10 C. and maintained at this temperature while 22.7 parts of technical orthoethoxy-benzoyl chloride are added dropwise over a period of about minutes. As will be seen from the resultant precipitation, reaction occurs largely durin this interval. Stirring is maintained for an additional 15 minutes at 810 C. and then for about 1% hours at room temperature. The reacted mixture is diluted to volume of about 500 parts of water and stirred for an additional V; hour. Isolation of the product is obtained by filtering out the precipitate, washing the latter with 2% potassium carbonate solution, and then with a small amount of water. Finally, drying is carried out at C. An excellent yield of good quality product is obtained.

Example 2 Example 1 was repeated. However, in order to show thesuperiority of the use of potassium carbonate, in this experiment, sodium carbonate solution( 20% solution for addition of the acid binder and 2% solution for washing purposes) was substituted for the potassium carbonate solution. Additional amounts were added intermittently during acylation, as were required in order to keep the slurry alkaline. The resultant weight yield is slightly less than half the yield obtained in Example 1.

Example 3 Example 3 was performed, using sodium carbonate instead of potassium carbonate. The resulting weight yield was reduced by more than half.

Example 5 12.6 parts of 4,4'-diaminostilbene-2,2'-disulfonic acid is dissolved in 86 parts of water containing 5.9 parts of 50% sodium hydroxide solution, 53 parts of acetone, and a solution of 17.9 parts of potassium carbonate in 30 parts of water. This is cooled to 10 andgradually treated with 15 parts of o-anisoyl chloride. When acylation is complete, the reaction mixture is diluted and filtered. An excellent yield of the acylated product is obtained.

Example 6 Example 5 is performed in the same way, using sodium carbonate instead 01' potassium carbonate. The yield 01' product is very substantially inferior.

Example 7 To a solution resulting from mixing at 20 C. 16.7 parts by weight of 4,4-diamino-stilbene- 2,2'-disulfonic acid, 7.5 parts of 50% caustic soda solution and 87.1 parts of potassium carbonate, is slowly added with stirring, a solution of 19.3 parts of p-nitrobenzoyl chloride dissolved in 31.6 parts of acetone. The experiment is continued as in Example 1, except that 39 parts of additional potassium carbonate solution is added to maintain alkalinity. The product is obtained in substantially quantitative yield.

Example 8 Example 7 was repeated, substituting sodium carbonate for the potassium carbonate. A much lower yield of the product is obtained.

I claim:

1. In a process of reacting, in aqueous medium, 4,4-diamino-sti1bene-2,2'-disu1fonic acid with a carboxylic acid chloride of the benzene series, whereby hydrochloric acid is liberated, the improvement which comprises carrying out the reaction at a temperature of from 5 C. to 40 C. in the presence of potassium carbonate to act as acid binder for the liberated hydrochloric acid.

2. A process according to claim 1 in which the aqueous medium contains acetone.

3. A process according to claim 1 in which the carboxylic acid chloride is substituted by an alkoxy group.

4. A process according to claim 1 in which the carboxylic acid chloride is o-ethoxybenzoyl chloride.

5. A process according to claim 1 in which the carboxylic acid chloride is p-methoxybenzoyl chloride.

WENDELL PHILIP MUNRO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,823,743 Kalischer et al Sept. 15, 1931 2,104,595 Schirm Jan. 4, 1938 2,308,640 Bergmann et a1. Jan. 19, 1943 2,465,067 Conner et al. Mar. 22, 1949 2,468,431 Eberhart et a1 Apr. 26, 1949 FOREIGN PATENTS Number Country Date 442,530 Great Britain Feb. 10, 1936 Switzerland Sept. 15, 1943 

1. IN A PROCESS OF REACTING, IN AQUEOUS MEDIUM, 4,4''-DIAMINO-STILBENE-2,2''-DISULFONIC ACID WITH A CARBOXYLIC ACID CHLORIDE OF THE BENZENE SERIES, WHEREBY HYDROCHLORIC ACID IS LIBERATED, THE IMPROVEMENT WHICH COMPRISES CARRYING OUT THE REACTION AT A TEMPERATURE OF FROM -5* C. TO 40* C. IN THE PRESENCE OF POTASSIUM CARBONATE TO ACT AS ACID BINDER FOR THE LIBERATED HYDROCHLORIC ACID. 